[llvm] [VPlan] Passing non-null instruction when creating VPReductionRecipe in unit test. NFC (PR #120053)

[Florian Hahn via llvm-commits]

fhahn wrote:

After recent changes to https://github.com/llvm/llvm-project/pull/120054 IIUC the patch won't be needed any longer?

https://github.com/llvm/llvm-project/pull/120053